Trifluoroacetic Acid‐Induced Adsorption Dipole Modulation of Perylene Diimide Dipole Moment Enables 19.5% Efficiency in Binary Organic Solar Cells

Abstract Perylene diimides (PDIs) have emerged as promising materials for cathode interfacial layers (CILs) in organic solar cells (OSCs) due to their advantageous energy level alignment with active layer and insensitivity to film thickness, enabling the easy fabrication of efficient and large‐area devices. However, the inherent low dipole moment of PDIs results in suboptimal charge transport properties, limiting device performance. Herein, a new strategy by incorporating trifluoroacetic acid (TFA) into PDI material to fabricate a compound with a large number of dipole moments is introduced. Density functional theory calculations reveal that the highly electronegative F groups attract the ammonium end groups of PDIN and significantly increase the dipole moment of PDIN from 0.3 to 2.6 Debye, enhancing charge transfer in OSCs. By optimizing the TFA concentration to 2% in the PDIN layer and using the compound as CILs, champion efficiencies of 18.0% and 19.5% are achieved for state‐of‐the‐art binary active layers comprising PM6:Y6 and PM6:L8‐BO (Layer‐by‐Layer), respectively. Notably, these devices maintain 88.3% of their initial efficiency after 240 h, demonstrating exceptional operational stability. The work shows that the F‐induced adsorbed dipole strategy not only provides a new mechanism for material design but also paves the way for achieving high‐efficiency and stable OSCs.